Internal shoe drum brake



F. G. PARNELL INTERNAL SHOE DRUM BRAKE Jah. 25, 1949.

Filed June 50, 1945 FWZ l Jan. 25, 1949. F. G. PARNl-:LL

INTERNAL sHoE DRUM BRAKE 2 Sheets-.Sheet 2 Filed June 3o, 145

Patented Jan. 25, 1949 INTERNAL SHOE DRUM BRAKE Frank Gordon Parnell, Leamington Spa, England, assigner to Automotive Products Company Limited, Leamington Spa, England Application June 30, 1945, Serial No. 602,559 In Great Britain June 30, 1944 11 Claims.

This invention .relates to internal shoe drum brakes, and more particularly to brakes of the kind (hereinafter mentioned as the kind` referred to) in which a pairof brake shoes are free to move circumferentially between abutments on a supporting member so that each shoe, when moved outwards against the drum, engages with that'abutment towards which it is urged by the rotation of the drum, so that both shoes act as leading shoes in each direction of drum rotation.

Broadly speaking, the object of the invention is to provide a simple brake of the above kind, which operates efiiciently and has a relatively small number of parts.

An object of the invention Vis to provide an internal shoe drum brake of the kind referred to in Which the shoe-spreading mechanism is operated at a single point to spread both shoes simultaneously into contact with the drum.

Another .object .is to provide a brake in which common adjusting means areprovided for the brake shoes and the shoe-spreading mechanism.

The invention is illustrated by way of example in the accompanying drawings, in which:

Figure 1 is a transverse sectional view of a two leading shoe brake assembly;

Figure 2 is a fragmentary sectional plan taken on the line 2--2 of Figure l;

. Figure 3 is a fragmentary sectional elevation taken on the line 3-3 of Figure 1 and Figure 4 is a fragmentary transverse elevation showingf aA modied construction of adjusting means used to compensate for Wear of the shoe linings. f

The brake assembly is built up upon a nonrotatable supporting member 40, which latter is conveniently mounted upon the end of the usual axle casing II by means of bolts I2, as is shown in Figure 2. A cylindrical drum I3 surrounds the supporting member I and is rotatable with the. Wheel or equivalent (not shown) requiring to be braked. For this purpose a pair of rigid arcuate shoes, indicated generally at I4 and I5, are mounted upon the supporting member I0 and are provided with lining members IS arranged to be pressed against the internal `surface of the drum I3 when the shoes I4 and I5 are expanded, as will be hereinafter explained. Each of the shoes comprises a ange-portion I8 to which the lining vI 6 is secured and from which .a Pair o1 webs extend inwards in substantially parallel planes, as will be seen in Figure 3, where the webs are indicated at IS. At each end of each shoe these webs I9 are curved in shape and are engageable with abutment surfaces which act as Vanchorages when the brake is in operation.

Thus, as shown in Figure l, the left-hand end of the shoe M1 is engageable with an anchorage member 20 mounted upon a projecting part 2| of the supporting member I0; the anchorage member 2B has a narrow middle portion 22 which fits loosely between the webs iii-of the shoe I4, the rounded ends of said shoe Webs being arranged to engage with a pair of lateral projecting portions or steps formed on the anchorage member 2B, the operative surface of one of said projecting portions or steps being indicated in dotted lines at 23. At the opposite end of the shoe I 4 the two Web portions I9 engage similarly with an abutment member 24, which latter fits between said webs I@ and has a pair of lateral projections or steps for engagement by said web portions, one of said projections or steps being shown with its operative surface at 25. The abutment member 24 is arranged to be adjustable in position and for this purpose it is internally screw-threaded for engagement by a right-hand screw-thread 3| upon the upper end of a stem 26, which is pivy otally mounted within a bore 2l formed in the supporting member Hl. ,The stem 26'has an integral worm wheel 23 in engagement with a worm 29 upon an adjusting spindle 30, the arrangement being such that as said adjusting spindle Si) is turned the stem 25 is caused to move angularly at a much slower rate, thus providing a ne and powerful adjustment for positioning the abutment memberA 24. The stem 26 is extended below the worm wheel 28 and is formed at 32 with a left-hand Soren/thread engaging an abutment member 33 for the right-hand end of -the shoe i5, the abutment member 33 being similar in construction to the abutment member 24 and having oneof its pair of operativev surfaces indicated at 34. The other end of the shoe I5 engages With an anchorage member 35 which is similar to the anchorage member 20 and is formed with a pair` of loperative surfaces, one of which is shown at 36, for engagement by the left-hand end of the shoe i5. The shoes i4 and I5 are connected together by ,coiled tension springs 31 and 38 which draw the shoes towards one another so that when the brake is released the ends of the shoes engage with the abutment surfaces 23, 25, 34 and 35.

VThe shoes I4 and I5 are moved into engagement with the drum i3 by expanding mechanism comprising a lever 45 which is pivoted to the sup-k port member Il? at 48, asis shown in Figure 2. The lever is arranged to be moved in an anticlockwise direction by an alternative means, namely either hydraulically by a liquid pressure motor unit 41 or mechanically by la tension brake rigging, the end part of which is shown at 48 and is connected to the lever 45 by a pin 49 slidable within a slot 5l). At its other end the lever 45 is formed with a transverse bore 5| Vwitllfin a somewhat cylindrical thrust block 52 Ais slidably mounted, said thrust bloei; being prevented from rotation by a grub screw 53, the tip'of which engages a longitudinal groove 54 in the thrust block. At its ends the thrust block .152 is iori'iied take up slack in the toggle linkage 51, 6|, 65. It will be seen that with this form of mounting the outer parts of the elbow members 6| and 62 are free to move within limits circumferentially of the brake and at the same time said elbow members are capable of exerting an outward force upon the corresponding brake shoes through the medium of the semi-circular projections such as 1| and 8|. Y Y

When the brake is applied anti-clockwise movement ci the actuating lever 4:l5 causes the thrust block 52 at the inner e'nd of said lever to be moved radially inwards towards the aii's of the Ybrake with the result that the pairs of thrust rods 51, 65 and 58, 56 push the elbow members "61YV and 52 Voutwards, thus overcoming the force of thesprings 31 and 38 and bringing the shoes.

T4 and |15 into engagement with the rotating brake dru-'m "|3. I f the drum is rotating in a -clc'mkw'ise 'direction 'the brake shoe I4 moves cirn cumferentially with it until the webs of said shoe thrust rods `55 and 55, and these in turn have their` opposite ends engaged within recesses v61 and 5E inthe abutment members 24 and 33, respectively. The thrust rod 51, elbow member 6| and thrust rod 65 together constitute -a toggle linkage for applying the shoe I4, whilezthe corresponding t'ogglelinkage for the shoe i5 is, of course, comprised bythe two thrust rods 58 and 6 6 lacti-ng in conjunction with the elbow member 62. Y Y 1 Y The manner in which the elbow member S2 is operatively connected with the lshoe I5 is shown in Figure 3; the elbow member 6| is arranged in an exactly similar way. The elbowmember 52 is substantially-U-shaped in radial-section and its limbs 69 and 1I) are formed atrtheir extremities with substantially semi-circular projections 1| and 12 arranged to engagepivotally with core responding semi-'circular notches or recesses 13 and 1,4 vformed inthe edges of the brake shoe Vwebs i9. At its opposite part the elbow member 62 is fitted with a-pin 15 forming 'an anchorage for a coiled tension spring 16, wh'ich latter has its opposite end connected with the support member Ill, as indicated at 11. Thus 'the 'spring 15 urges the elbow member B2 radially inwards, 'as far fas permitted by the thrust rods 58 and 657, while at the saine time the two 'springs 31 and 38 Ypull the brake shoe `|5 inwards s'o'as to main; tain the recesses 13 and 14 vin intimate engagement with the projections 1| and 12. To steady the shoe |15 againstY movement in 'a directionV parallel with the axisioi -the brake' the support member I0 isformed adjacent the elbow member 62 with a lpair of fingers 18 and v19 extending across theouter 'surfaces `Vof the shoe webs I9. The nger 19 is i'itted with a spring-pressed plunger "8D arranged to hold the brake shoe resiliently against the nge'r 18. Y

The elbow member 6| is similarly vformed with apair of semi-circular projections, 'oneof -which is `seen at 8| in Figure land engages witnasemicircular recess '82 in the corresponding web I9 of the brake shoe I4; the elbow member 6|' is pulled inwards vvby ka tension 'spring 83* adapted to come /ih-to engagement with the anchoring surfaces 25 of the abutment member 24, thus enablig 'the shoe i4 toY act as a leading shoe; at the same time clockwise movement of the shoe I5 brings its webs `into yengagement with the abutment "surfaces V35 'of :the 'anchorage VAmember 35 so "that 'it also acts 'as a leading shoe. YOrith'e Vother hand 'if'the drum I3 is rotating in an anti-clockwise direction 'theshoes j| 4 and '|15 move in the opposite ydirections and anchor, respective*- ly, upon the abutment Vsurfaces 23 and'34. During the normal life or the Abrake the linings 'it become progressively worn, "giving a large brake clearance and consequently necessitating an lex'- cessive free 4n'iovemen't of the actuating lever "-45 before the shoes come -into engagement with the brake 'd-r-1nnf| 3. IThis clearance is reduced Eby turning the adjustment spindle 30, which, through the "screw-threads -`3| and 32,;moves 'the abutment members -24 and 33 "apart: itV will be noted that this not only presses 'the shoes 5f4 and l5 outward-s, VAowing to -inoveinent -of the abutment surfaces 25 and 34,-butalso correspondingly shifts the Vrecesses `(i1 and v|58 so as to 'takelup slack-in the two toggle linkages. Y

l As, when the brake is applied, the toggle flink-h agefs eiirtiafsubstantial thrust lin a radial direction upon the abutment Y'members v24 rand @33, "it

may be desirable in some cases to use the-construction shown in Figure 4 as this Lenables "the shear stress inthel stem r2li to 4bet avoided, vfor at least considerably reduced. The support member 5|@ lis forined 'with a pair of bearing surfaces 84 and `85 which extend parallel with Ethe *screw* lil-Headed 'stem `26 andr'which are 'Sli'ably enedged Aloythefabiitr'ne'ntirnenfiber's 24 and 33.

' It will be `VIAunderstood 'that the arrangements which have been described are given Ymerelyby w'ayof example and that various `modiii'cations may-be fm'ade'in the construction of 'the fbrake. For instance,` it may be desirable in Isome cases to 'use the toggle llinkage arrangement "with only one o'f 'the shoes, different-applying means Abeing employed Afor thefs'econd shoe.

what Ifciaim is: Y

"1y-'An internal shoe drum brake of the kind referred to Tand including la supporting 'member for "the brake, wherein lshoe expanding inechai'sm fo'r'f-at least `one oi the l'shoes comprises j'a Veshjaped 'toggle linkage extending along th'e shoejcorinecting means between said 'toggle -lirrkage and Alth'eshce inthe region of Ethe elbow of the toggle linkage, said-'connecting fmeahs befiiig 'the sole cennectin-between A'the toggle link age and the shoeand being connected to the shoe intermediate the Yeiidsof vsaid shoe, abutment means for one end of said linkage on-the supporting member of the brake for transmitting the thrust from said end of the toggle linkage to said supporting member/means for adjusting said abutment means, and actuating meansto move the other end of said toggle-linkage towardssaid abutment, .soas to cause the elbow of. the toggle linkage to force the shoe outwardsinto engagement with'the drum.

2. An internal shoe drum brake of the kind referred to, wherein shoe-expanding mechanism is provided comprising a pair of toggle linkages, abutments for one end of each of the toggle linkages, a single actuating means for moving the other ends of the toggle linkages inwards towards the brake axis, thereby spreading the elbows of the toggle linkages apart, connecting means between said toggle linkages and the shoes whereby the spreading of the toggle linkages moves the shoes outwardly into contact with the drum, and connecting means between the toggle linkages and the actuating means comprisingv a thrust block which is moved radially inwards to apply the brake and is slidable in a circumferential direction to equalize substantially the applying forces produced by the toggle linkages.

3. An internal shoe drum brake of the kind referred to, wherein shoe expanding mechanism is provided comprising a pair of toggle linkages, abutments for one end of each of the toggle linkages, a single actuating lever, a thrust block connecting the actuating lever to the toggle linkages and slidably mounted in a passage eX- tending transversely through the inner end of the actuating lever so as to be movable radially inwards to apply the brake and slidable in a circumferential direction to equalize substantially the applying forces produced by the toggle linkages, and connecting means between said toggle linkages and the shoes whereby the spreading of the toggle linkages moves the shoes outwardly into contact with the drum.

4. An internal shoe drum brake of the kind referred to, wherein shoe expanding mechanism for at least one of the shoes comprises a V-shaped toggle linkage extending along the shoe, and connected at or adjacent its elbow to the shoe intermediate the ends of the latter, one end of said linkage being anchored and the other end being moved by actuating means towards the said anchorage so as to cause the elbow of the toggle linkage to force the shoe outwards into engagement with the drum, the toggle linkage comprising a pair of thrust rods arranged in V-formation, their adjacent ends engaging in recesses formed in an elbow member, which latter is operatively connected with the shoe to exert outward force thereon but" is movable relative to the shoe so as to permit the thrust rod recesses to move circumferentially of the'Y brake.

5. An internal shoe drum brake as claimed in claim 4, wherein the elbow memberis pivotally engaged at its inner part by that portion of the web of the shoe nearest the axis of the brake, and the recesses are formed in the outer part of the elbow member and are disposed adjacent the usual lining ange of the shoe.

6. An internal shoe drum brake as claimed in claim 4, wherein the elbow member is urged radially inwards by a spring, thereby maintaining it in thrust-transmitting engagement with the thrust rods of the toggle linkage.

7. An internal shoe drum brake as claimed in` claim 4, wherein the elbow member is disposed between a pair' of webs o the brake shoe and has -apair vof aligned projections with curved surfaces engaging with recesses formed in the brake shoe webs.

8. An internal shoe drum brake as claimed in claim 4,'wherein the elbow member is disposed between a pair of webs of the brake shoe and has a pair of aligned projections with curved surfaces engaging with recesses formed in the brake shoe webs, the projections and the recesses for engagement thereby being all substantially semi-circular as seen parallel with the brake axis.

9. An internal shoe drum brake of the kind referred to, wherein shoe expanding mechanism for at ieast one of the shoes comprises a V-shaped toggle linkage extending along the shoe, connecting means between said toggle linkage and the shoe in the region oi the elbow of the toggle linkage, said connecting means being connected to the shoe intermediate the ends of said shoe, an abutment member for one end of the said linkage and serving as an anchorage for the toggle linkage, said abutment member being formed with an abutment surface which is engaged by the adjacent end of the corresponding brake shoe, and being located by adjusting means for setting the off position of the brake shoe and at the same time taking up slack in the toggle linkage, and actuating means to move the other end of said toggle linkage towards said abutment member, so as to cause the elbow of the toggle linkage to force the shoe outwards into engagement with the drum.

l0. An internal shoe drum brake of the kind referred to, wherein shoe expanding mechanism for at least one of the shoes comprises a V-shaped toggle linkage extending along the shoe, connecting means between said toggle linkage and the shoe in the region of the elbow of the toggle linkage, said connecting means being connected to the shoe intermediate the ends of said shoe, an abutment member for one end of the said linkage and serving as an anchorage for the toggle linkage, said abutment member being formed with an abutment surface which is engaged by the adjacent end of the corresponding brake shoe, and being engaged by a screw-threaded stem serving to move the abutment member towards the said brake shoe and actuating means to move the other end of said toggle linkage towards said abutment member, so as to cause the elbow of the toggle linkage to force the shoe outwards into engagement with the drum. l

1l. An internal shoe drum brake of the kind referred to, wherein shoe expanding mechanism Vfor at least one of the shoes comprises a V-shaped toggle linkage extending along the shoe, connecting means between said toggle linkage and the shoe in the region of the elbow of the toggle linkage, said connecting means being connected to the shoe intermediate the ends of said shoe, an abutment member for one end of the said linkage and serving as an anchorage for the toggle linkage, said abutment member being formed with an abutment surface which is engaged by the adjacent end of the corresponding brake shoe, and being engaged by a screw-threaded stem serving to move the abutment member Y towards the said brake shoe, a surface on the brake supporting member extending parallel to the axis of the stem, said abutment member sliding on sai-d surface and transmitting thereto the thrust exerted on the abutment member by Smm 7 th'toggle linkage as 'the brake is applied, tuating means t'o move the `'ozllr ed 'of said teggzle link-age towards said abutment .member s0-fas to cause the :elbow of tmI fwg'gle iinkage to force the shoe outwards into engagement with the drum. A

`GORDON PARNELL.

UNH-ED STATES xmrmfis Nwnber 

